Development or removal of block copolymer or PMMA-b-S-based resist using polar supercritical solvent

ABSTRACT

Methods of developing or removing a select region of block copolymer films using a polar supercritical solvent to dissolve a select portion are disclosed. In one embodiment, the polar supercritical solvent includes chlorodifluoromethane, which may be exposed to the block copolymer film using supercritical carbon dioxide (CO 2 ) as a carrier or chlorodiflouromethane itself in supercritical form. The invention also includes a method of forming a nano-structure including exposing a polymeric film to a polar supercritical solvent to develop at least a portion of the polymeric film. The invention also includes a method of removing a poly(methyl methacrylate-b-styrene) (PMMA-b-S) based resist using a polar supercritical solvent.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates generally to semiconductor fabrication,and more particularly, to methods for supercritical development orremoval of block copolymer for patterning applications. In addition, theinvention relates to removal of poly(methyl methacrylate-b-styrene)(PMMA-b-S) based resists using a polar supercritical solvent.

2. Related Art

The use of bottom-up approaches to semiconductor fabrication has grownin interest within the semiconductor industry. One such approachutilizes block copolymers for generating sub-optical ground rulepatterns. In particular, one illustrative use is forming a ‘honeycomb’structure with in a poly(methyl methacrylate-b-styrene) (PMMA-b-S) blockcopolymer. In the case of a cylindrical phase diblock having a minorcomponent of PMMA-b-S, the PMMA-b-S block can phase separately to formvertically oriented cylinders within the matrix of the polystyrene blockupon thermal anneal.

FIGS. 1A-C show the above-identified approach. FIG. 1A shows a substrate10 coated (optionally) with a random copolymer 12, which is affixed tothe surface. A block copolymer 14 is then coated on the top surface ofthe stack, as also shown in FIG. 1A. Block copolymer 14 is annealed withheat allowing for phase separation of the immiscible polymer blocks 18and 20, as shown in FIG. 1B. As shown in FIG. 1C, the annealed film isthen developed (perhaps augmented by using actinic irradiation) toreveal a pattern 30 that is commensurate with the positioning of one ofthe blocks in the copolymer. For simplicity, the block is shown ascompletely removed although this is not required.

Since block copolymers have a natural length scale associated with theirmolecular weight and composition, the morphology of a phase-separatedblock copolymer can be tuned to generate cylinders of a specific widthand on a specific pitch. In one approach, ultraviolet (UV) exposure isused to cause the PMMA to decompose (and polystyrene to crosslink) intosmaller molecules and, further, developed using glacial acetic acid toremove the small molecules. In other approaches, development simply usesthe acetic acid to reveal the pattern.

For most applications, and in particular bottom-up semiconductorfabrication methodologies, the pattern must be transferred to asubstrate. FIGS. 2A-B show a representative procedure in which asubstrate 40 and a dielectric material 42 deposited upon it are(optionally) coated with a random copolymer 44, which is affixed to thesurface. As shown in FIG. 2A, a block copolymer film 46 is coated on thetop surface of the stack, annealed with heat allowing for phaseseparation of the immiscible polymer blocks, and developed to reveal apattern having one block 48 remaining as a mask and voids 50commensurate with the position of a second block of copolymer film 46.Again, for simplicity, the block is shown as completely removed althoughthis is not required. This patterned copolymer film 46 is then used as amask to transfer into underlying dielectric material 42. As shown inFIG. 2B, the resulting patterned dielectric material 52 is commensuratewith the original pattern in copolymer film 46. This type of pattern hasbeen shown, when applied to cylindrical phase PMMA-b-S, to allow forincreased surface area, which increases capacitance in storageapplications as well as provides ‘quantized’ wells for flash memory.

While these approaches demonstrate the capability of bottom-upfabrication, there are challenges with respect to implementation in aconventional semiconductor fabrication facility. One challenge relativeto the implementation of this particular diblock copolymer is thedevelopment of PMMA-b-S without damaging a surrounding matrix whilemaintaining manufacturing compatible processes. In particular, theconventional approaches use glacial acetic acid to remove the PMMA-b-Susing batch processing or liquid coating. Glacial acetic acidimplementation requires specialized tooling in order to handle itsflammability and corrosiveness. In other approaches, isopropyl alcohol(IPA) is utilized to develop PMMA-b-S e-beam resist. Unfortunately, IPAis not sufficient to remove an unexposed PMMA-b-S film having molecularweights and compositions of interest for semiconductor fabrication.Additionally, in some circumstances a 25 J/cm² UV exposure is used todevelop the block copolymer, which is roughly 1000 times greater thanthat used for conventional resist.

Another challenge in the semiconductor industry is removingPMMA-b-S-based resist. In particular, plasma stripping of PMMA-b-S-basedresist can damage porous interlayer dielectrics in certain integrationschemes.

In view of the foregoing, there is a need in the art for methods ofdeveloping and/or removing select regions of block copolymers that donot suffer from the problems of the related art. In addition, there is aneed in the art for a method of removing PMMA-b-S-based resist withoutdamaging porous interlayer dielectrics.

SUMMARY OF THE INVENTION

The invention includes methods of developing and/or removing selectregions of block copolymer films using a polar supercritical solvent. Inone embodiment, the polar supercritical solvent includeschlorodifluoromethane, which may be exposed to the block copolymer filmusing supercritical carbon dioxide (CO₂) as a carrier orchlorodiflouromethane itself in supercritical form. The invention alsoincludes a method of forming a nano-structure including exposing apolymeric film to a polar supercritical solvent to develop at least aportion of the polymeric film. The invention also includes a method ofremoving a poly(methyl methacrylate-b-styrene) (PMMA-b-S)-based resistusing a polar supercritical solvent.

A first aspect of the invention is related to a method of removing aselect portion of a block copolymer, the method comprising the steps of:exposing the block copolymer to a polar supercritical solvent todissolve the select portion of the block copolymer; and removing thedissolved portion of the block copolymer.

A second aspect of the invention is directed to a method of forming anano-structure, the method comprising the steps of: forming a polymericfilm over a substrate; annealing the polymeric film to allow for phaseseparation of immiscible components; and exposing the polymeric film toa polar supercritical solvent to develop at least a portion of thepolymeric film into the nano-structure.

A third aspect of the invention is directed to a method of developing ablock copolymer in a semiconductor fabrication process, the methodcomprising the steps of: forming a block copolymer film upon a surface;and exposing the block copolymer film to a polar supercritical solventto develop the block copolymer.

A fourth aspect of the invention includes a method of removing apoly(methyl methacrylate-b-styrene) (PMMA-b-S)-based resist, the methodcomprising the steps of: providing a partially fabricated semiconductordevice including a porous dielectric and having the PMMA-b-S-basedresist over at least a portion of the partially fabricated semiconductordevice; and using a polar supercritical solvent to remove thePMMA-b-S-based resist.

The foregoing and other features of the invention will be apparent fromthe following more particular description of embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of this invention will be described in detail, withreference to the following figures, wherein like designations denotelike elements, and wherein:

FIGS. 1A-C show the formation of a diblock copolymer according to aprior art approach.

FIGS. 2A-B show the transfer of a diblock copolymer pattern into asubstrate according to a prior art approach.

FIGS. 3A-C show a method of forming a nano-structure incorporating amethod of developing and/or removing a block copolymer according to theinvention.

FIG. 4 shows an alternative step for the method of FIGS. 3A-C.

FIG. 5 shows an alternative step for the method of FIGS. 3A-C and 4.

FIG. 6 shows a method of removing a PMMA-b-S-based resist according tothe invention.

DETAILED DESCRIPTION

With reference to the accompanying drawing, FIGS. 3A-C show a method offorming a nano-structure incorporating a method of developing and/orremoving a select portion of a block copolymer according to theinvention. As used herein, “develop” means formation of patterns, and“remove” means taking out material from a film or other structure.

As shown in FIG. 3A, a first optional step includes coating a substrate100 with a random copolymer 110. “Random copolymers” includemacromolecules in which the probability of finding a given monomericunit at a given site in the chain is independent of the nature of theadjacent unit. Random copolymers are called random because the sequencedistribution of monomeric units follows is somewhat random, i.e., theydo not have an ordered form like diblock copolymer. For example, styrenemonomer does not have to repeat with methyl methycrylate, it could bestyrene itself. Random copolymer 110 is affixed to a surface ofsubstrate 100 and excess material is removed. A polymeric film 120,preferably a block copolymer, is then formed over substrate 100 andrandom copolymer 110, i.e., over the stack. Substrate 100 may include avariety of materials such as silicon, dielectric materials, etc. As usedherein, a “block copolymer” is any polymeric material includingimmiscible components used to generate a pattern on a substrate wherebythe pattern is not defined by a projected aerial image, i.e.,irradiation is not required for use. In one embodiment, block copolymer120 includes polystyrene, poly(methyl methacrylate-b-styrene) (PMMA-b-S)or blends thereof or any other block copolymers or polymeric blendcapable of phase separation. In an alternative embodiment, blockcopolymer 120 includes a diblock copolymer, i.e., having a moleculeincluding two immiscible polymer blocks A and B covalently bonded at oneend such as polystyrene and PMMA-b-S. In another embodiment, a portionof block copolymer 120 may be crosslinked. Block copolymer 120 may beused to transfer the pattern onto a lower layer, as described aboverelative to FIG. 2B.

As shown in FIG. 3B, block copolymer 120 (FIG. 3A) is then annealed 130to form annealed block copolymer film 144, and allow for phaseseparation of immiscible components of block copolymer 120 into blocks140 and 142 (block 142 being referred to hereafter as “developed block142”). Exposure to actinic irradiation to develop block copolymer 120may offer certain benefits such as cross linking the polystyrene while‘breaking’ PMMA-b-S polymer chains; hence, enhancing solubilityproperties further once exposed to supercritical polar solvents.

As shown in FIG. 3C, annealed block copolymer film 144 is then developedby exposing it to a polar supercritical solvent 150 to reveal a pattern160. This step dissolves a select portion, i.e., developed block 142(FIG. 3B), of block copolymer 120 (FIG. 3B), which is made into solublePMMA-b-S by the polar supercritical solvent. As used herein,“supercritical” means that the solvent is able to sustain a chainreaction in such a manner that the rate of reaction increases, orincreases the solubility properties of a solvent due to increase indensity at or above the critical temperature and pressure. In oneembodiment, polar supercritical solvent 150 may include at least one of:chlorodifluoromethane, methylene chloride, 1,1 dichloroehylene, ethylenedichloride, chloroform, 1,1 dichloroethane, trichloroethylene,chlorobenzene, O-dichlorobenzene, tetrahydrofuran, dibenzyl ether,acetone, methyl ethyl ketone, cyclohexanone, diethyl ketone,acetophenone, methyl isoamyl ketone, isophorone, methyl acetate, ethylformate, ethyl acetate, diethyl carbonate, diethyl sulfate,2-ethoxyethyl acetate, 2-nitropropane, nitrobenzene, pyridine,morpholine, analine, N-methyl-2-phyrrolidone and cyclohexylamine. In onepreferred embodiment, polar supercritical solvent 150 includeschlorodifluoromethane. In this case, the exposing step preferably occursat a temperature of greater than approximately 96.4° C. and a pressuregreater than approximately 48.5 bars. Polar supercritical solvent 150may also contain an optional co-solvent such as ethanol or methanol. Inone embodiment, this step may include using supercritical carbon dioxide(CO₂) as a carrier for the polar supercritical solvent 150, but this isnot necessary.

The exposing step, shown in FIG. 3C, may also include tuning polarsupercritical solvent 150 to dissolve block 142 (FIG. 3B), i.e., tuningthe supercritical polar solvent and the process environment. Forexample, in one embodiment, the exposing occurs in an environment at atemperature of no less than approximately 31° C. and no greater thanapproximately 80° C., and a pressure of no less than approximately 200bar and no greater than approximately 300 bar.

As also shown in FIG. 3C, a next step may include removing the dissolveddeveloped block 142 (FIG. 3B) to form nano-structure 170. Developedblock 142 is shown as completely removed (open area 162) for simplicity.It should be recognized, however, that developed block 142 does not haveto be removed from block copolymer 144 to reveal pattern 160.

Referring to FIG. 4, a nano-structure 200 is illustrated over asubstrate 202. Nano-structure 200 includes diblock copolymer film 220after development, but without a developed block 242 (actually surroundsblock 240) removed. The method of forming nano-structure 200 includesthe same steps shown in FIGS. 3A-3B. However, block copolymer 220 isannealed with heat and without actinic irradiation allowing for phaseseparation of the immiscible polymer blocks. Next, block copolymer 220is developed using a polar supercritical solvent (not shown) to form apattern 260 having an insoluble block 240 and a soluble block 242 thatis commensurate with the positioning of one of the blocks in blockcopolymer 220. As shown, soluble block 242 is covalently bound toinsoluble block 240.

Turning to FIG. 5, an optional step for either embodiment describedabove (shown only for the FIG. 4 embodiment) may include transferring apattern 260 of nano-structure 200 (block copolymer) into underlyingsubstrate 202, for example, via an etch 280 to create openings 282. Thetransfer renders the substrate porous, i.e., the porosity is caused bythe transfer of the pattern similarly to the porosity described in USPatent Application Publication No. 20040127001. Openings 282 can be usedto form semiconductor devices, semiconductor interconnects, microfluidic arrays, micro-fuel cell or any substrate requiring anano-perforated film known to those skilled in the art. Nano-structure200 can be removed once openings 282 are completed.

The above-described methods allow development of a block copolymer andremoval of a selected portion (developed block 142) adjacent to asubstrate 100. Where substrate 100 is in the form of a dielectric layer,e.g., a porous dielectric, the methods allow removal of a selectedportion without physically damaging the dielectric, as shown in FIG. 4.

Turning to FIG. 6, the invention also includes a method of removing apoly(methyl methacrylate-b-styrene) (PMMA-b-S)-based resist 300 from apartially fabricated semiconductor device 302 having PMMA-b-S-basedresist 300 thereon. PMMA-b-S-based resist 300 can be provided, as shownin FIG. 5, as nano-structure 200 or as a typical resist layer, as shownin FIG. 6. The method includes providing partially fabricatedsemiconductor device 302 including a dielectric 304 and havingPMMA-b-S-based resist 300 over at least a portion of the partiallyfabricated semiconductor device, and using a polar supercritical solvent306 to remove PMMA-B-S-based resist 300. As in earlier embodiments,polar supercritical solvent 306 may include at least one of:chlorodifluoromethane, methylene chloride, 1,1 dichloroehylene, ethylenedichloride, chloroform, 1,1 dichloroethane, trichloroethylene,chlorobenzene, O-dichlorobenzene, tetrahydrofuran, dibenzyl ether,acetone, methyl ethyl ketone, cyclohexanone, diethyl ketone,acetophenone, methyl isoamyl ketone, isophorone, methyl acetate, ethylformate, ethyl acetate, diethyl carbonate, diethyl sulfate,2-ethoxyethyl acetate, 2-nitropropane, nitrobenzene, pyridine,morpholine, analine, N-methyl-2-phyrrolidone and cyclohexylamine. In onepreferred embodiment, polar supercritical solvent 306 includeschlorodifluoromethane. In this case, the exposing step preferably occursat a temperature of greater than approximately 96.4° C. and a pressuregreater than approximately 48.5 bars. Polar supercritical solvent 306may also contain an optional co-solvent such as ethanol or methanol. Inone embodiment, this step may include using supercritical carbon dioxide(CO₂) as a carrier for the polar supercritical solvent 306, but this isnot necessary. The method allows for removal of PMMA-b-S-based resist300 without damaging porous dielectric 304.

While this invention has been described in conjunction with the specificembodiments outlined above, it is evident that many alternatives,modifications and variations will be apparent to those skilled in theart. Accordingly, the embodiments of the invention as set forth aboveare intended to be illustrative, not limiting. Various changes may bemade without departing from the spirit and scope of the invention asdefined in the following claims.

1. A method of removing a select portion of a block copolymer, themethod comprising the steps of: exposing the block copolymer to a polarsupercritical solvent to dissolve the select portion of the blockcopolymer, wherein the block copolymer includes a block polystyrene andpoly(methyl methacrylate b-styrene) copolymer; and removing thedissolved portion of the block copolymer.
 2. The method of claim 1,wherein the block copolymer includes a diblock copolymer.
 3. The methodof claim 1, wherein the exposing step includes using supercriticalcarbon dioxide (CO₂) as a carrier for the polar supercritical solvent.4. The method of claim 1, wherein the exposing step includes exposing inan environment at a temperature of no less than approximately 31° C. andno greater than approximately 80° C., and a pressure of no less thanapproximately 200 bar and no greater than approximately 300 bar.
 5. Themethod of claim 1, wherein the polar supercritical solvent includes atleast one of: chlorodifluoromethane, methylene chloride, 1,1dichloroehylene, ethylene dichloride, chloroform, 1,1 dichloroethane,trichloroethylene, chlorobenzene, O-dichlorobenzene, tetrahydrofuran,dibenzyl ether, acetone, methyl ethyl ketone, cyclohexanone, diethylketone, acetophenone, methyl isoamyl ketone, isophorone, methyl acetate,ethyl formate, ethyl acetate, diethyl carbonate, diethyl sulfate,2-ethoxyethyl acetate, 2-nitropropane, nitrobenzene, pyridine,morpholine, analine, N-methyl-2-phyrrolidone and cyclohexylamine.
 6. Themethod of claim 1, further comprising the step of tuning the polarsupercritical solvent to dissolve a select region of the blockcopolymer.
 7. The method of claim 1, wherein a portion of the blockcopolymer is crosslinked.
 8. The method of claim 1, wherein the polarsupercritical solvent includes chlorodifluoromethane at a temperature ofgreater than approximately 96.4° C. and a pressure greater thanapproximately 48.5 bar.
 9. The method of claim 1, wherein the removingstep includes removing only a portion of the block copolymer from theblock copolymer film.
 10. The method of claim 1, wherein the removingstep includes removing the block copolymer adjacent to a dielectric. 11.The method of claim 1, further comprising the step of transferring apattern of the block copolymer into an underlying substrate.
 12. Themethod of claim 11, wherein the transferring step renders the substrateporous.